Low power actuator and valve-actuator combination

ABSTRACT

Actuators and valve-actuator combinations are disclosed which require low power for actuation, and which are particularly suitable for use to control a valve associated with a pipeline. Such an actuator ( 20 ) comprises a thrust member ( 26 ) moveable between two end of travel positions, an annular rotor having magnetic poles, an annular magnetisable stator having at least one winding and poles with which the rotor poles are aligned in each of a plurality of rotational positions of the rotor relative to the stator, and a drive connection between the rotor and the thrust member which is adapted to convert rotational movement of the rotor into linear movement of the thrust member. The actuator is able to hold its position using minimal energy, and may be located within or around an associated pipe.

FIELD OF THE INVENTION

This invention concerns actuators and valve-actuator combinations whichrequire low power for actuation. More particularly, it concerns devicesof these types which can be employed for example to control the openingand closing of a valve in a pipe to control the flow of fluids in thepipe, to cover and uncover an opening in the wall of a pipe, or topermit, to control the rate of, or to prevent flow along a pipe.

BACKGROUND TO THE INVENTION

Oil extraction from the seabed is now substantially more difficult thanhitherto, and operators are now forced to follow a ‘brownfield’ strategyand extract oil from poorly yielding fields. As a consequence a low-costinflow control valve to manage flows in existing, as well as futuremulti-lateral installations, is now called for. Additionallyenvironmental and economic considerations, both sub-sea and on thesurface, make it increasingly important to have a capability rapidly toshut off flow in the event of pipeline leak or rupture.

Pipes may range in diameter from a few inches to more than three feet.Typically pipes bringing oil to the surface are 5″ inside diameter, andinflow control valves may be slid into position along such a pipe andsecured in place adjacent an opening in the pipe wall it is to control.In other applications where the valve is to control flow along a pipe,the valve may be installed at the time of pipeline construction, or maybe fitted subsequently, within the pipe.

Previously suggested solutions have involved relying on a hydraulic lineto operate a valve associated with a pipeline. However, such a line canonly function effectively over a limited distance.

The present invention seeks to provide an actuator which is able to holdits position using minimal energy.

The invention also seeks to provide a valve and actuator combinationwhich will operate in an adverse environment in remote locations wherethere is only limited availability of electric or hydraulic power.

Furthermore, the present invention seeks to provide an actuator, and avalve and actuator combination which can be fitted into and moved alonga pipe for positioning as required, in which energy is stored locally toassist operation of the actuator and therefore the opening and closingof the valve.

SUMMARY OF THE INVENTION

The present invention provides an actuator comprises a thrust membermoveable between two end of travel positions, an annular rotor havingmagnetic poles, an annular magnetisable stator having at least onewinding and poles with which the rotor poles are aligned in each of aplurality of rotational positions of the rotor relative to the stator,in which the rotor poles remain attracted to a set of stator poles untila current is caused to flow in the at least one winding, which altersthe magnetic field acting between the rotor and stator polessufficiently to cause the former to be repelled from the stator poleswith which they are currently aligned and to be attracted to and alignedwith another set of stator poles, and a drive connection between therotor and the thrust member which is adapted to convert rotationalmovement of the rotor into linear movement of the thrust member.

The actuator may include first spring means which acts on the thrustmember and is compressed or stretched from its relaxed length as therotor rotates such that, while the spring means is at least partlycompressed or stretched, the spring force acting on the thrust membercombines with the thrust exerted thereon due to the rotation of therotor through the drive connection to enhance the actuating forceexerted by the thrust member.

The invention further provides an actuator comprises a thrust membermoveable between two end of travel positions, a rotor having magneticpoles, a magnetisable stator having at least one winding and poles withwhich the rotor poles are aligned in each of a plurality of rotationalpositions of the rotor relative to the stator, in which the rotor polesremain attracted to a set of stator poles until a current is caused toflow in the at least one winding, which alters the magnetic field actingbetween the rotor and stator poles sufficiently to cause the former tobe repelled from the stator poles with which they are currently alignedand to be attracted to and aligned with another set of stator poles,first spring means which acts on the thrust member and is compressed orstretched from its relaxed length as the rotor rotates, a driveconnection between the rotor and the thrust member which prevents linearmovement of the latter under the action of the spring means except whenthe rotor rotates and is adapted to convert rotational movement of therotor into linear movement of the thrust member such that, while thespring means is at least partly compressed or stretched, the springforce acting on the thrust member combines with the thrust exertedthereon due to the rotation of the rotor through the drive connection toenhance the actuating force exerted by the thrust member.

This enhancement of the magnetic thrust force will continue until thespring reaches its relaxed length.

In a preferred embodiment of an actuator according to the presentinvention, the actuator is arranged so as to define a hollow spacethrough it, which extends through a central opening defined by the rotorand/or stator. In use it may be located within a pipe. Alternatively, itmay be provided around an associated pipe, with the rotor and statorsurrounding (and preferably coaxial with) the pipe, in order to reducethe radial extent of the outline of the actuator. This facilitates itsinsertion into a borehole. It may be mounted on the outercircumferential surface of a section of pipe which can then be includedat an appropriate place in a pipeline. The rotor may be spaced axiallyfrom the stator with respect to its axis of rotation.

Preferably, the drive connection converts rotational movement of therotor into linear movement of the thrust member in a directionsubstantially perpendicular to the plane of the rotor.

Preferably, the actuator includes control means for supplying pulses ofcurrent to the at least one winding so that the rotor can beprogressively rotated in one direction or the other.

The control means may be adapted to supply electric current to thestator winding in controlled bursts, each of which causes the rotor tospin at high speed, and the inertia of the rotating rotor is releasedvia a bi-stable drive transmission device between the rotor and thedrive connection to provide higher thrust forces than would be createdsimply by the rotation of the rotor under load.

By successively decoupling the rotor from the drive connection after theinertia is spent, and allowing the rotor to accelerate again beforere-establishing the connection between rotor and drive connection, asequence of impact thrusts can be created.

A succession of such impact thrusts when the spring means is fullycompressed (or stretched) will produce a sequence of very high impactthrusts at the beginning of a full movement of the actuator, which willprogressively reduce in impact as the spring extends (or becomes lessstretched) and the thrust member moves under the action of the rotorrotation.

Preferably, there is a second spring means also acting on the thrustmember but in the opposite sense to the first spring means, which willbe compressed or stretched in the opposite sense to that of the firstspring means when the rotor rotates.

A battery may be incorporated into or located close to the actuator tosupply the operating current.

Where there is a second spring means to be compressed (or stretched) asthe thrust member moves towards the opposite end of its travel, thecontrol means may be adapted to instigate a similar sequence of highimpact thrusts each of which exerts sufficient force on the secondspring means to compress (or stretch it) as the thrust member is movedtowards and into its other end of travel position.

The actuator may form part of, or act on, a flow control valve, and theinvention also provides a combination of actuator as aforesaid and avalve, which can be opened and closed in response to control signals, tocontrol the flow of a fluid through the valve.

Where a valve and actuator combination embodying the invention is to beinstalled in a pipe for subterranean use, as in oil fields for exampleto control the flow of oil and other fluids from the field into thepipe, it must be capable of operating at or below the seabed and underthe high ambient pressure which exists at those depths.

The invention is not limited to seabed locations and a valve andactuator combination may be located on land or at the surface of the seafor controlling the flow of fluid through a pipe.

The actuator retains or can harness and store energy in the form ofpotential mechanical energy in the compressed or stretched spring means,as potential magnetic energy in the permanent magnet means, and aselectrical energy in a rechargeable battery or other electric energystorage device. All the stored energy can be used for actuating thevalve.

A key feature of an actuator embodying the invention is that it onlyrequires electrical power when it is commanded to move. Its powerconsumption while in a resting state is zero. During actuation, energyused in overcoming friction is expended irrecoverably, but depending onthe work required to be done by the actuator during actuation, much ofthe energy which is converted into movement of a closure device can berecovered, and stored if a second spring means is employed, to assist insubsequent operation of the actuator. In this way, demand for electricalpower from a battery or other source can be significantly reduced.

Effectively therefore, where little energy is required to actually movea valve closure device once freed from an open or closed condition, mostof the energy required for each operation of the actuator is thatrequired to overcome friction and to accelerate any object (such as avalve closure device) that is to move.

The actuator is particularly suited to operating a sleeve valve.

Such a valve may be incorporated within a cylindrical sleeve containingin one or more annular compartments one or more batteries, the actuator,and the spring means.

Preferably the compartments are sealed against ingress of liquid and maybe filled with an incompressible fluid such as an oil, to allow thecompartments to withstand excessive crushing pressures as can existunderground and at or below the seabed.

Typically springs are provided at both ends of the section of the sleevewithin which the thrust member moves.

It is to be understood that the invention is not limited to actuation ofsleeve valves and an actuator as proposed may be applied to valves inwhich the valve closure is for example a ball or butterfly.

To ensure the valve will open or close on command, it is important thatthe actuator is capable of overcoming ‘stiction’ forces betweenrelatively movable parts of the valve, such as relatively slidablemembers. To this end, a clutch or lost motion connection is preferablyprovided between a rotor and the thrust member (or between the latterand a valve closure), to allow momentum to be developed by for examplerotation of the armature before that movement is applied to move a valveclosure device.

Preferably, the design of the valve also permits mechanical operationusing an intervention tool, so that it will retain functionality and canbe opened or closed mechanically after battery life is exhausted, or inthe event of a communication failure, or a battery failure, or damage.

Preferably, the actuator or valve is adapted to be operated using awireline tool, with only inductive coupling between tool and actuator orvalve. This allows long term control of the valve to be envisaged evenin a permanently installed situation, where perhaps the battery and/orelectronics have failed.

Lithium-ion batteries may be employed as the batteries. However theinvention is not limited to the use of any particular battery andrenewable energy sources may also be employed.

Depending on the application, the current source may only be required todeliver electrical energy for a relatively small number of actuations(open or close) over a period of as long as five years. In someapplications, the number of actuations may be as small as twentyactuations in five years.

Typically, the control means comprises an electronic control circuitwhich is compatible with being controlled via electromagneticsignalling, or other types of signalling, or by command from a localmonitoring system.

It is of course important that such a control circuit will respond to acommand to operate even after extended periods of remaining inactive.

A force multiplying means may be provided to magnify the force exertedby the rotor but demagnify its movement. More particularly, a forcemultiplying means is provided between the rotor and the thrust member.Alternatively, or in addition, a force multiplying means may be providedbetween the thrust member and a body to be moved by the actuator, suchas a valve closure.

The force multiplying/movement demagnifying means may be mechanical,such as a bottle screw, a cam and cam follower arrangement, or ahydraulic pump using the principle employed in a vehicle braking orclutch operating system, where large pedal travel with relatively smallforce is converted into a much larger force at the brake or clutchcylinder albeit with very much smaller displacement.

In configurations using a hydraulic force multiplying means, theactuator may be operable to hold a valve closure at its fully open orclosed positions, or at intermediate positions therebetween.

In a preferred embodiment, the force multiplying means between thethrust member and a valve closure is a hydraulic pump, and the output ofthe pump is connected to two control valves, the control valves beingconnectable to respective ports of a further main valve to feed fluidselectively to one or both ports to control the main valve.

Pressure sensing means may be provided in combination with a forcemultiplying means, where the force multiplying means is in the form of ahydraulic pump, to output a signal responsive to the pressure at thepump output to control means, the control means being able to determineinformation regarding the valve closure status and/or positiontherefrom.

Where the valve is such that it will normally remain closed or open forlong periods of time in polluted sea water and/or crude oil environment,solid particles such as sediments, and vegetation may penetrate insidethe outer sleeve. Corrosion can also occur. Solid particles andcorrosion can resist any sliding movement of the inner sleeve within theouter sleeve. It is for that reason that the initial movement of theinner sleeve may require quite a substantial linear force acting betweenthe sleeves to free it.

After the inner sleeve has been freed and axial movement is possiblesediments and corrosion will be crushed or moved so permitting ongoingmovement of the inner sleeve, and in general much less force is neededto continue the displacement of the inner sleeve as it moves towardsanother stable position. This, arises because in the majority ofapplications for this type of valve, the pressure difference across thevalve is relatively small, and the valve itself is balanced, meaningthat main flow or leakage flow is spread evenly around the inner sleeve.

Incorporating an actuator embodying the present invention in a remotelocation, which may be inaccessible, to operate a fluid flow controlvalve, should result in:

-   -   Reduction in intervention;    -   Reduction in workovers;    -   Reduction in risk and exposure of personnel and associated        health and safety issues;    -   Retro-fit zone control will optimise production with low capital        outlay;    -   Economic use of horizontal and multilateral completions, with        the resultant step change in production efficiency, and modest        capital outlay;    -   Reduced environmental risk.

A primary application for the actuator is in the operation of a remotelylocated valve in an oil well pipeline. In an existing pipeline this canreduce the risk of asset damage in severe cases.

By dimensioning the actuator or the valve and actuator combination sothat the device is a sliding fit within or around such a pipeline, orinto a borehole, the device can be installed in situ, or for exampleretrofitted to an existing pipeline.

Embodiments of the invention will now be described by way of example,with reference to the accompanying schematic drawings, wherein:

FIGS. 1A and 1B show cross-sectional side views of a valve and actuatorcombination according to a first embodiment of the invention;

FIG. 2 shows cross-sectional side views of a valve and actuatorcombination according to a second embodiment of the invention;

FIG. 3 shows a partial diagrammatic view of the rotor and stator of theactuator of FIG. 2;

FIG. 4 shows a diagrammatic view of an alternative rotor and statorconfiguration to that of FIG. 3;

FIGS. 4A and 4B are tables indicating how the coils shown in FIG. 4 areenergised in use;

FIG. 5 is a perspective side view of an actuator according to a secondembodiment of the invention;

FIG. 6 is a cross-sectional side view of the actuator of FIG. 5; and

FIG. 7 is a block diagram representing a hydraulic force multiplier foruse in combination with the actuator of FIGS. 5 and 6.

In the embodiment shown in FIGS. 1A and 1B, the valve consists of anouter fixed sleeve 10 and an inner sliding sleeve 12. A sealedcompartment 14 is provided at both ends of the outer sleeve. Only one isshown in the drawing. The one at the other end is similar and may beprovided merely for symmetry or may also house an actuator arrangementas fitted within 14, as will be described later. Where it houses anactuator, it will operate in the opposite sense on the inner sleeve 12so that if one acts to drive the sleeve 12 up, the other will act todrive it down.

After installation in a pipeline, the outer sleeve 10 is sealed to theinside of the pipe using contact-expansion seals, for example.

Holes 16, 18 typically of 22 mm diameter are arranged around thecircumference of both the inner and the outer sleeves. Fluid can flowtherethrough when the sets of holes 16, 18 are aligned. Flow can beprevented by moving the inner sleeve so that the holes 18 no longeralign with the holes 16. If the holes are arranged in circular linesaround the sleeves, the movement can be radial, so that holes 18 in 12are rotated out of or into alignment with holes 16 or can be linear(axial) so that the line of holes 18 becomes axially aligned or is movedaxially out of alignment with the line of holes 16.

The inner sleeve 12 is moved relative to the outer sleeve 10 to open orclose the valve. As shown the actuator drives the sleeve 12 axially, butother actuators may be employed which will merely rotate the innersleeve 12 relative to the outer sleeve 10, so as to rotationally alignor misalign the two sets of holes. In this case the inner sleeve 12remains axially in the position shown in FIG. 1A.

Within the compartment 14 is arranged a battery 6, a controller 8, anelectromagnetically triggered magnetic actuator 20, and a bistablecoupling device 22 such as a clutch, which only requires pulses ofelectrical energy to change it from one stable condition with the platesengaged to its other stable condition with the plates disengaged. Aforce multiplier 24, such as a bottle screw or similar or a hydraulicdrive, which magnifies the force to be transmitted inversely to thedisplacement, is also located within 14, and an annular thrust member 26extends between 24 and inner sleeve 12, for transmitting force to thelatter to move it axially as required. The force multiplier can eithertransmit force in a circular sense to assist in circular rotationalmovement of 12 relative to 10, or can transmit force axially to assistin axial movement of 12 relative to 10.

Permanent magnet means (not shown) within the actuator 20 magneticallylocks an armature means (not shown in detail) to hold a spring (notshown) in a compressed state while an opposed spring (not shown) isrelaxed.

Valve operation is achieved by the combination of electromagnetic force(which may not be large) and the force obtained when the compressedspring is released, so causing the inner sleeve 12 to slide from a firstposition to a second position. Total operation time could take up to 30seconds if a large number of incremental steps are required to extendthe spring from its relaxed state, and longer if subsequently it is tocompress another spring (not shown).

The battery, electronic control circuit, mechanical linkages, and thespring or springs for storing energy are housed in the or each sealedcompartment 14 at one or both ends of the sleeve 10.

The energy stored in the spring or springs combines with theelectromagnetic actuator force so as to overcome any initial staticfriction or ‘stiction’ forces, which may be considerable if the valvehas been left unoperated for a long time, and has become contaminatedwith solids or corrosion or both.

It has been found that a force of 250 kg will normally be sufficient asan initial impulsive force for freeing a stuck valve of the type used ina pipeline at or below the seabed. However, since operational conditionsare difficult to predict, the valve actuator is preferably designed toproduce up to 5,000 Newtons (about 510 kg), which is approximately twicethe normally expected maximum force needed.

A capacitor may be trickle-charged from a battery or batteries, toprovide pulses of current to a solenoid type winding which willinfluence the magnetic flux linking the or each armature, toincrementally move the latter in response to each capacitor discharge inapplications in which valve/actuator combinations provided by theinventor are to be employed.

Incremental armature movement translates into a ratchet action, in whicheach step is powered by a discharge from the capacitor, so as toprogressively compress one of the springs (while allowing the other torelax) so that the former is ready for the next valve actuation.Typically this process could take up to 15 minutes or longer. Theactuator then remains in a steady state, drawing no electric power,until it receives the next command to operate by releasing thecompressed spring.

Battery capacity is selected so as to provide sufficient current for atleast the expected number of complete cycles, preferably with a safetyfactor of 50% or more.

Battery power is also required for the electromagnetic signallingcircuitry, which is preferably TTL input compatible. However, withappropriate circuit design, it should be possible to keep the currentdrain to the circuitry to very low levels so as to achieve the target ofa 5-year life for the valve.

Where battery power is inadequate for such a long period, one or more ofthe batteries may be of a rechargeable type and the actuator/valve mayinclude means for generating an electric charging current, either fromfluid flow in the pipe or by electromagnetic induction from a probeintroduced down the pipe when required.

The actuator therefore operates in three modes. In one mode itincrementally compresses a spring to store energy which is thenavailable to assist at least the start of a subsequent actuation. In asecond mode it produces a constant but smaller force for driving athrust member to effect the desired actuation, and in a third mode thecompressed spring force is added to the constant smaller driving forceproduced by the rotor rotating when under load, to assist in dislodginga valve closure from an open or closed condition in which contaminationor corrosion is preventing the closure from moving.

Preferably magnetic latching is employed to hold the spring in itscompressed condition.

Stretching a spring will also store energy and the invention is notlimited to compression of spring(s) but includes arrangements in which aspring or springs is/are instead stretched by the incremental movementof the actuator.

Principal design parameters of a valve/actuator are:—

Operating pressure 10,000 psi ambient Differential pressureapproximately balanced Operating temperature 150° C. initially, target200° C. Diameter 5 inch tubing based Drift diameter 4.151 inches Minimuminternal valve diameter 3.0 inches Travel 1 inch (25.4 mm) Length 60inches max Force to move sleeve 5,000 Newtons Maximum actuation time 30seconds Minimum interval between actuations 15 minutes Electrical energyrequired to hold Nil position Number of actuations from battery 20 (10complete cycles) Housing and valve material approved stainless steel

In the event of failure of the battery, an intervention tool on awireline can be inserted. Using magnetic coupling, the valve closure oractuator can be moved so as to open or close the valve.

Although only a sleeve valve primarily for closing off an inlet from anoilfield into a pipeline has been described in detail, the invention isnot limited to such valves. Other types of valve may be operated usingthe same principle of storing energy over a relatively long period oftime in two forms, partly in stored mechanical energy (typically in acompressed or extended spring), and partly as electrical energy. Bothtypes of stored energy are then available to operate an actuator andopen or close a valve in response to some signal which may be deliveredfrom a control centre as a result of human intervention or may beautomatically generated in response to some change in a parameter, suchas pressure or temperature or flow rate linked to the pipeline. Thus,the invention may be employed to operate for example gate valves, ballvalves or butterfly valves.

In the alternative embodiment shown in FIGS. 2 and 3, the valve is againcomprised of two cylindrical sleeves (100, 102), the inner sleeve (102)being axially slidable within the outer sleeve (100).

A sealed annular housing (104) is located at the upper end of the outersleeve (100), which contains a battery in a first annular compartment(106) and an electronic controller in an axially spaced annularcompartment (108).

Below the compartment (108) is located an annular magnetisable stator110 around which are arranged a plurality of windings one of which isshown at (112) and another at (114). The windings and stator are alsoshown in FIG. 3, which is a diagramatic edge view of the stator polesshown in close proximity to those of the annular rotor (or armature)116. In FIG. 3, the edge view is flattened for the purposes ofillustration, although the stator (110) and rotor (116) are curved. Theaxis about which the rotor rotates is parallel to the plane of the papercontaining FIG. 3, as it is also in FIG. 2.

Attached to the underside of the annular rotor (116) is a friction ring(118) so that it rotates with the rotor.

An annular clutch including an annular clutch plate (not shown) is shownat 120. This is rotably fitted around the inner sleeve (102). If theplate is forced into contact with this friction ring (118), the clutchrotates with the rotor.

The clutch has an operating mechanism which is bistable in that energyis only required to move it from an engaged state (with the frictionring (118) and clutch plate (120) in contact) to a disengaged state (inwhich 118 and 120 are out of contact) and will remain in whichever stateit has last been triggered.

The rotor (116) is mounted within cylindrical bearings one of which isshown at (122) fitted within the outer sleeve (100).

The nut 124 is, like the rotor, mounted within cylindrical bearings(128, 130) within the outer sleeve (100), and its internal thread isengaged on an external complimentary screw thread profile (132) formedaround an annular enlargement (134) on the outer face of the innersleeve (102).

The nut (124) extends axially over a greater length than the annularenlargement (134) so that as it is rotated it will axially traverse thethreaded enlargement (134).

The inner and outer sleeves (100, 102) are keyed so that whilst theinner sleeve can slide axially relative to the outer, no relativerotation is possible between 100 and 102.

Annular thrust devices (136) and (138) are secured within the outersleeve (100) and two helical springs (140, 142) are shown trapped inseries between them. The springs are in fact separated by a driving ring(144) attached to and extending radially from the inner sleeve (102) sothat as the latter slides axially relative to the outer sleeve (100) onespring will become compressed and the other will be allowed to relax. Asshown the sleeve (102) is at the lower end of its travel and spring(140) is uncompressed and spring (142) is fully compressed.

Rotation of nut (124) so as to raise the inner sleeve (102) relative tothe outer sleeve (100) will gradually cause spring (140) to becomecompressed and allow spring (142) to expand. The inner sleeve (102) iscarried in a linear bearing (146) which ensures smooth sliding of thesleeve (102) relative to the outer sleeve (100), and allows the sleeve(102) to be a clearance fit within the compartment (104) at the upperend of the sleeve (100) and within the internal face of the lower end ofthe sleeve (100).

Annular seals at 148, 158 and 152, 154 allow sliding movement of 102 butprevent not only the ingress of liquids but especiallyparticulates/solids such as sand.

As previously mentioned, the valve shown in FIG. 2 is adapted to bepushed along a cylindrical pipeline within which it is a loose slidingfit, until the ring of openings (156) in the outer sleeve register withone or more similar openings in the wall of the pipeline (not shown). Atthis point the outer sleeve (100) is secured in position within thepipeline using a contact expansion seal or the like (not shown).

The inner sleeve has a similar ring of openings (158), whichcircumferentially align with those in the outer sleeve, but can bedisplaced axially out of alignment with the openings (156) by axialsliding of the inner sleeve (102) relative to the outer sleeve (100), aspreviously described.

In the scrap view of FIG. 3, permanent magnets (160, 162, 164 etc.) areshown mounted around the rotor (116) between poles (166, 168, etc.). Inthis arrangement the rotor itself is constructed from non-magnetisablematerial.

The poles (166, 168 etc.) are spaced around the rotor (116) in a similarmanner to the spacing of poles (170, 172, 174, 176, etc.) which protrudeaxially from the underside of the magnetisable stator ring (110).Windings such as 114 are located between the poles (170, 172 etc.) andare connected by cables to the control unit (108) so that current can besupplied thereto, when required, to alter the magnetic polarity of thestator poles and cause the rotor to rotate until the fixed magneticpolarity rotor-poles align with oppositely magnetically polarisedstator-poles.

Since the magnets (160, 162 etc.) are permanent and produce a powerfulmagnetic field between the adjoining stator and rotor poles, once therotor has rotated into registry with another set of stator poles, thecurrent to the windings can be removed. The powerful magnetic field inthe air gaps between the stator and rotor poles serves to lock the rotorrotationally relative to the stator. This locking is sometimes referredto as cogging and is not a positive mechanical lock but with appropriatechoice of air gap, magnetic materials and strength of the magnets (160,162 etc.), a very high torque will be needed to rotate the rotor from acogged position to the stator. Put another way, the magnetic coggingforce acts like a friction brake on the rotor.

As previously mentioned, an actuator embodying the invention enables asubstantial linear force to be generated by combining three energysources so as that all act together for some of the time. The threecomprise spring energy, the inertia of a rotating rotor, and electricenergy from the battery.

In the scrap view of FIG. 4, permanent magnets (178, 180, 182, 184) areshown mounted around the rotor (116) with alternating polarity.Preferably, each rotor pole is associated with two stator poles. In thisexample, four rotor poles are provided. The rotor (116) is constructedfrom magnetisable material preferably a ferromagnetic material, asopposed to the non-magnetic material from which the rotor (116) in FIG.3 can be constructed.

Also shown in FIG. 4 is the stator ring (110) which is also constructedfrom magnetisable material.

Eight poles (186, 188, - - - 198, 200) protrude axially from theunderside of the stator ring (110). Windings A-H are located around thestator poles and are connected by cables to the control unit (108) sothat current can be selectively supplied thereto, as required, tomagnetically polarize the stator poles so as to cause the rotor to slideto the left or the right until each permanent magnet rotor-pole onceagain aligns with a pair of stator-poles.

Since the rotor poles (178, 180 etc.) are permanent magnets and the airgap between rotor and stator poles is small, a powerful magnetic fieldexists between the adjoining stator and rotor poles and once the rotorhas rotated into registry with another set of stator poles, the currentto the windings (A, B, C, etc.) can be removed. As with the FIG. 3arrangement, the powerful magnetic field in the air gaps between thestator and rotor poles serves to lock the rotor rotationally relative tothe stator (sometimes referred to as cogging), and as with FIG. 3, thisis not a positive mechanical lock but with appropriate choice of airgap, magnetic materials and magnetic strength of the magnets (178, 180etc.), a very high torque will again be needed to rotate the rotor froma cogged position.

The tables in FIGS. 4A and 4B indicate how the coils in FIG. 4 are to beenergised and the direction of rotation is achieved.

Compressed spring (142) acts directly on a ring (144) attached to theinner sleeve (102). The inertia energy in the fast rotating rotor (116)and friction disc (118) is added to the spring force as soon as therotating components are connected via the bi-stable clutch (120) to therotatable nut (124).

The latter is mounted within the outer sleeve in bearings (128, 130)axially separated by a spacer (131), and the nut (124) is axiallylocated by the bearings so that relative linear (axial) movement betweenit and outer outer sleeve. (100) is prevented. In this way, therotatable nut (124), which is coupled to the inner sleeve (102) by meansof interengaging threads (126, 132), provides substantial linear forcepushing the inner sleeve (102) axially along the outer sleeve (100).This interengagement creates a force multiplying effect.

The sum of the three sources of energy when the clutch is engagedprovides a sudden axial force or impulse, which will normally initiatemovement of the inner sleeve relative to the outer to begin valveclosure or opening.

In cases of severe contamination in which the inner sleeve is so jammedwithin the outer sleeve that on initial engagement of the clutch (120)there is significant resistance to axial movement of the sleeve, theclutch can be disengaged to allow the rotor to run up to speed beforeengaging the clutch again, and the process can be repeated until thebond created by the contamination or corrosion is broken as the impactforces crush and move away any movement-locking sediments.

Freeing the sleeves will be referred to as a first phase of the actuatormovement.

Thereafter rotation of the battery driven rotor, acting through theinterengaging threads, together with the remaining energy stored in thespring (142), provides enough axial force to continue to move the innersleeve (102) axially within the outer sleeve.

This will be referred to as the second phase of the actuator movement.It occurs as the inner sleeve continues to move relative to the outersleeve, now largely free from friction, using electric energy from thebattery to rotate the rotor and maintain axial movement of the thrustmember even after the spring force which assists in the initial movementhas reduced to zero.

During a third and final phase of the movement, the second spring (140)becomes compressed so as to store energy to be available to assistreverse movement of the inner sleeve at a future time.

It is unlikely that the battery will have the capacity to provide theenergy to perform this compression by rotating the rotor under theincreasing load created as the spring is compressed, and this finalphase will probably be performed over an extended period of time, bymaking use of the inertia in the rotating rotor and friction disc onceagain.

In order to do so, the clutch is disengaged to clear the rotor and allowit to spin up to speed, after which the clutch is engaged, and thecombination of the inertia energy and the continuing torque created bythe electric current from the battery flowing in the stator windingsacts via the high ratio gearing of the interengaging threads to begin tocompress the spring. As soon as the inertia energy is exhausted and therotor decelerates under load, the clutch is disengaged, the rotor isfree to spin up to speed again, and the process of re-engaging and thendisengaging the clutch is repeated.

In theory there is no limit to how many times this process of clutchengagement and disengagement can be performed, but typically the mostefficient driving strategy is determined by the control means (108) andis adopted and executed in a flexible way as appropriate.

Once the inner sleeve reaches its final position at which the spring(140) is now fully compressed, there is no further requirement forelectric current from the battery.

The valve position is secured by the permanent magnet locking effectbetween rotor and stator created by the permanent magnet and theplurality of interacting rotor and stator poles. As previously describedthe magnetic poles create a cogging effect so that the rotor has a largenumber of positions in each of which it will be held stationery by themagnetic cogging effect. Since the magnets are permanent, the rotor willremain in any one of these stable positions without the need forelectrical energy to be supplied, in the same way as the rotor of astepper motor is held stationary.

To further save battery energy, the controller (108) is adapted torevert into a sleep mode requiring virtually zero power, after the innersleeve has reached a final end position. However, since it is necessaryto be able to trigger the control means into activity when the actuatoris next to operate, a communication monitoring system within thecontroller (108), albeit requiring only a minute current to keep itoperating, remains electrically active until the device is next requiredto operate.

When a request signal is received to change the valve position, thecontroller (108) can thereby be reactivated.

Where the valve and actuator are to be located and operated in a highambient pressure environment, the internal actuator mechanism is sealedwith double seals (148, 150) and (152, 154) and any space between thesleeves is filled with a clean, air-free incompressible fluid such as anoil. In this way the actuator and seals are largely protected againstmechanical damage due to high ambient pressure, as could otherwiseoccur.

The invention may therefore provide a valve and actuator combinationwhich will operate in an adverse environment in remote locations wherethere is only limited availability of electric or hydraulic power.

Another actuator configuration 298 embodying the present invention isshown in FIG. 5. It is arranged so as to be mounted around a pipe 300and fit within an annular volume surrounding the pipe, so that it canpass along and be installed in a borehole with the pipe. Pipework andwiring associated with the actuator itself have been omitted from FIG. 5for the purposes of clarity.

The actuator has an annular stator 302 which includes a plurality ofpoles spaced around it and extending axially from it that haverespective coils 304 associated with them. The stator poles face polepieces and magnets of a rotor 306, in a similar manner to precedingembodiments. A sleeve 308 has a circumferential groove formed in itsouter surface which defines an annular cam 309. The sleeve is mounted onor integrally formed with part of rotor 306, and are together rotatablysupported on pipe 300 by bearings 307.

Within a housing 310 on each side of the actuator, a plunger pusher 312is mounted so as to be axially slideable. A cam follower pin 304 extendsradially inwards from the plunger pusher so as to engage with cam 308.Plunger pusher 312 is connected to a plunger 314 which extends axiallyout of housing 310 and into a pump assembly 316. Plunger pusher 312 andplunger 314 together form a thrust member.

The two cam follower pin and plunger assemblies are provided on oppositesides of the actuator to exert balanced, symmetrical forces on therotor, for smoother operation.

A pack 318 containing electronic control means and a battery pack forthe actuator is provided adjacent to the stator 302.

As shown in FIG. 5, alongside the pump assemblies 316, two dual valves320 and 322, a single valve 324 and a hydraulic fluid reservoir 326 arecircumferentially spaced around the pipe. Their function will bedescribed with reference to FIG. 7.

In use, the pump assemblies 316 are coupled to a main valve (not shown)which is arranged to control flow associated with the pipe 300. Rotationof rotor 306 by energising poles of stator 302 as described aboverotates cam 308, which in turn displaces cam pin 314, plunger pusher 312and plunger 314 axially. This increases the pressure in pump assembly316. Each rotation of rotor 306 creates a high pressure pulse in thepump assembly which is employed to operate the main valve.

The actuator illustrated in FIGS. 5 and 6 employs two force multipliersto develop a large actuation force, which may be required to dislodge amain valve closure stuck in position following a long period ofinactivity for example. To operate a big hydraulic sleeve valve forexample, substantial force is required, typically in the region of 5000Nto 50000N.

The first force multiplier is a mechanical one where the angle of therotating cam acts like a wedge. In this case, the linear tangentialpulling force is multiplied by the wedge ratio, which in this case,where two synchronous pumps are used, is equal one quarter of theannular cam length divided by the plunger linear travel distance. Takinga 100 mm rotor diameter and 9 mm plunger linear travel, the ratio isabout 9.

The second force multiplier is hydraulic. Plunger 314 is relativelysmall, typically 5 to 10 mm diameter or 20 to 80 mm² plunger area, andis hydraulically connected with a large piston of the main valve,typically having an area of 1500 to 2000 mm². The force multiplicationratio is equal to the piston plunger area ratio, which in this exampleis in the region of 25 to 75.

In this example, the total force multiplication could be in the regionof 225 to 675. This way, using a 500 times force multiplier, 1 tonne or10000N force can be achieved with 2 kg or 20N rotating force. In apreferred embodiment, the rotating force is generated by 16 coils.Therefore only 0.12 kg or 1.2N force per coil is needed to achieve asubstantial pulling force to operate the main sleeve valve.

In some situations, when the main valve is exposed to sea water for along time, solidified sediments can make it difficult to initiate thevalve movement. To overcome this problem, the force multipliers can besupported by effective use of rotor inertia. It would be beneficial tostart running the annular motor with a high pressure release valve open.Therefore the annular motor can gain some rotation speed because thepumps are running freely. In this way, kinetic energy of the rotor canbe steadily built up. At a certain moment, the release valve is closedand both pumps are driven with additional strength provided by inertia.The pressure is built up almost instantly to level sufficient toovercome sticktion of the sleeve valve. In some cases as much as 5000psi hydraulic pressure is needed. Once the sleeve valve starts moving,almost 10 times less hydraulic pressure is needed to maintain the valvemovement, typically 500 psi. Such a modest pressure can be easilyobtained from pumps driven by the battery powered annular actuator.

FIG. 7 is a block diagram of the hydraulic pump force multiplier of theactuator 298 shown in FIGS. 5 and 6. Single valve 324 is a high pressurerelease valve. Dual valves 320 and 322 have high and low pressure fluidpaths. The high pressure paths are connected (via high pressure supplylines shown by solid lines in FIG. 7) to the pump assemblies 316 ofactuator 298. The low pressure return paths are connected (via lowpressure lines shown as dotted lines) back to reservoir 326. The outputsof the high pressure paths through valves 320 and 322 are connected viarespective check valves 340 and 342 to respective hydraulic ports 344and 346 of a main valve 348, which is in the form of a push-pull typesleeve valve, for example. The battery pack 318 a and control unit 318 bof the pack 318 shown in FIGS. 5 and 6 are shown separately in FIG. 7.

By selectively applying high pressure pulses via the ports 344, 346, theactuator can move the valve closure (not shown) of main valve 348 oneway or the other, lock it in a given position, or leave it floating andfreely moveable for maintenance purposes, for example.

In FIG. 7, two pressure sensors are shown as coupled to the highpressure line, a DC sensor 350 and an AC sensor 352. Signals generatedby these sensors are fed back to control unit 318 b to provideinformation regarding the status and/or position of the valve closure ofmain valve 348.

For example, as noted above, an initial very high pressure pulse may beemployed to dislodge the valve closure. However, if the sensors indicatethat the initial high pressure does not fall away, this suggests thatthe closure may still be jammed. It may then be appropriate to reapply arelatively large magnitude pulse using momentum built up again by therotor, as discussed above.

Once the valve closure is moving under the control of the actuator, eachrotation of the actuator rotor will generate two pressure pulses, aseach pin 304 follows the two axial oscillations of the cam surface 309per rotation. The control means may count these pulses to determine theposition of the valve closure of main valve 348.

1. An actuator comprising a thrust member moveable between two end oftravel positions, an annular rotor having magnetic poles, an annularmagnetisable stator having at least one winding and poles with which therotor poles are aligned in each of a plurality of rotational positionsof the rotor relative to the stator, in which the rotor poles remainattracted to a set of stator poles until a current is caused to flow inthe at least one winding, which alters the magnetic field acting betweenthe rotor and stator poles sufficiently to cause the former to berepelled from the stator poles with which they are currently aligned andto be attracted to and aligned with another set of stator poles, and adrive connection between the rotor and the thrust member which isadapted to convert rotational movement of the rotor into linear movementof the thrust member.
 2. An actuator as claimed in claim 1, includingfirst spring means which acts on the thrust member and is compressed orstretched from its relaxed length as the rotor rotates such that, whilethe spring means is at least partly compressed or stretched, the springforce acting on the thrust member combines with the thrust exertedthereon due to the rotation of the rotor through the drive connection toenhance the actuating force exerted by the thrust member.
 3. An actuatorcomprising a thrust member moveable between two end of travel positions,a rotor having magnetic poles, a magnetisable stator having at least onewinding and poles with which the rotor poles are aligned in each of aplurality of rotational positions of the rotor relative to the stator,in which the rotor poles remain attracted to a set of stator poles untila current is caused to flow in the at least one winding, which altersthe magnetic field acting between the rotor and stator polessufficiently to cause the former to be repelled from the stator poleswith which they are currently aligned and to be attracted to and alignedwith another set of stator poles, first spring means which acts on thethrust member and is compressed or stretched from its relaxed length asthe rotor rotates, a drive connection between the rotor and the thrustmember which prevents linear movement of the latter under the action ofthe spring means except when the rotor rotates and is adapted to convertrotational movement of the rotor into linear movement of the thrustmember such that, while the spring means is at least partly compressedor stretched, the spring force acting on the thrust member combines withthe thrust exerted thereon due to the rotation of the rotor through thedrive connection to enhance the actuating force exerted by the thrustmember.
 4. An actuator as claimed in claim 1 which is arranged so as todefine a hollow space through it, which extends through the rotor andstator.
 5. An actuator as claimed in claim 2, wherein a second springmeans also acts on the thrust member, but in the opposite sense to thefirst spring means, which will become compressed as the first springmeans extends due to movement of the thrust member towards one of itsend of travel positions, and vice versa.
 6. An actuator as claimed inclaim 5, including control means for supplying pulses of current to theat least one winding so that the rotor can be progressively rotated inone direction or the other.
 7. An actuator as claimed in claim 6,wherein the control means is adapted to instigate a sequence of highimpact thrusts, each of which exerts sufficient force on the secondspring means to compress it as the thrust member is moved to its otherend of travel position.
 8. An actuator as claimed in claim 6, whereinthe control means is adapted to supply electric current to the statorwinding in controlled bursts, each of which causes the rotor to spin athigh speed, and the inertia of the rotating rotor is released via abi-stable drive transmission device between the rotor and the driveconnection to provide higher thrust forces than would be created simplyby the rotation of the rotor under load.
 9. An actuator as claimed inclaim 8, wherein the rotor is successively decoupled from the driveconnection after the inertia is spent, thereby allowing the rotor toaccelerate again before re-establishing the connection between rotor anddrive connection, so that a sequence of impact thrusts is created. 10.An actuator as claimed in claim 1, wherein an electric energy storagedevice is incorporated into or located close to the actuator to supplythe operating current.
 11. An actuator as claimed in claim 10, whereinthe storage device is a rechargeable device.
 12. An actuator as claimedin claim 10, wherein the storage device is a Lithium-battery.
 13. Anactuator as claimed in claim 1 which forms part of, or acts on, a flowcontrol valve.
 14. A combination of an actuator as claimed in claim 2,and a valve, which valve can be opened and closed by the actuator tocontrol the flow of a fluid through the valve.
 15. A valve and actuatorcombination as claimed in claim 14 adapted to operate at or below theseabed and under the associated high ambient pressure.
 16. A valve andactuator combination as claimed in claim 14 which is arranged to controlfluid flow into or out of a pipe, wherein the pipe is electricallyconductive, and operation of the actuator can be instigated byelectromagnetic signals or by using the pipe as a conductor ofelectricity.
 17. A valve and actuator combination as claimed claim 14,wherein the actuator stores energy in the form of potential mechanicalenergy in the compressed (or stretched) spring means, as potentialmagnetic energy in permanent magnet means, and/or as electrical energyin an electric energy storage device, and the stored energy is availableto actuate the valve.
 18. A valve and actuator combination as claimed inclaim 17, wherein kinetic energy of the actuator thrust member and valveclosure is recovered during actuation and stored in the second springmeans, to assist in subsequent operation of the actuator.
 19. A valveand actuator combination as claimed in claim 14 wherein the valve is asleeve valve.
 20. A valve and actuator combination as claimed in claim14, wherein the valve is incorporated within the cylindrical outline ofa sleeve containing at least one annular compartment containing theactuator.
 21. A valve and actuator combination as claimed in claim 20,wherein the art least one compartment is sealed against ingress ofliquid.
 22. A valve and actuator combination as claimed in claim 21,wherein the at least one compartment is filled with an incompressiblefluid, to allow the compartment to withstand high pressures as can existunderground and at or below the seabed.
 23. A valve and actuatorcombination as claimed in claim 20, wherein springs are provided at bothends of the section of the sleeve within which the thrust member moves.24. A valve and actuator combination as claimed in claim 14, in whichthe actuator or the valve can be operated using an intervention tool, sothat it will retain functionality and can be opened or closedmechanically, after battery life is exhausted, or in the event of acommunication failure, battery failure, or damage.
 25. A valve andactuator combination as claimed in claim 24, wherein the actuator orvalve is adapted to be operated using a wireline tool, with onlyinductive coupling between tool and actuator or valve, to allow longterm control of the valve even in a permanently installed situationwhere the battery and/or control system have failed.
 26. A valve andactuator combination as claimed in claim 14, wherein the valve andactuator is a sliding fit within or around an oil well pipeline.
 27. Avalve and actuator combination as claimed in claim 26, wherein thecombination is retrofitted to an existing pipeline.
 28. An actuator, ora valve and actuator combination, as claimed in claim 1, including aclutch or lost motion connection between the rotor and the thrustmember, or between the thrust member and a valve, to allow momentum tobe developed by rotation of the rotor before that movement is applied tomove a valve closure. combination is retrofitted to an existingpipeline.
 28. An actuator, or a valve and actuator combination, asclaimed in claim 1, including a clutch or lost motion connection betweenthe rotor and the thrust member, or between the thrust member and avalve, to allow momentum to be developed by rotation of the rotor beforethat movement is applied to move a valve closure.
 29. An actuator, orvalve and actuator combination, as claimed in claim 1, in which a forcemultiplying means is provided to magnify the force exerted by the rotorbut demagnify its movement.
 30. An actuator, or valve and actuatorcombination, as claimed in claim 29, wherein a force multiplying meansis provided between the rotor and the thrust member.
 31. An actuator, orvalve and actuator combination, as claimed in claim 30, wherein theforce multiplying means is provided by the drive connection of theactuator.
 32. An actuator, or valve and actuator combination, as claimedin claim 29, wherein a force multiplying means is provided for operationbetween the thrust member and a body to be moved by the actuator.
 33. Anactuator, or valve and actuator combination, as claimed in claim 29,wherein the force multiplying means is in the form of a bottle screw, acam and cam follower, or a hydraulic pump.
 34. An actuator, or valve andactuator combination, as claimed in claim 33, wherein the forcemultiplying means between the thrust member and a valve closure is ahydraulic pump, and the output of the pump is connected to two controlvalves, the control valves being connectable to respective ports of afurther valve to feed fluid selectively to one or both ports to controlthe valve.
 35. An actuator, or valve and actuator combination, asclaimed in claim 33, wherein the force multiplying means between thethrust member and a valve closure is a hydraulic pump, and the output ofthe pump is coupled to pressure sensing means for outputting a signalresponsive to the pressure at the pump output to control means, thecontrol means being able to determine information regarding the valveclosure status and/or position therefrom.